Magnetic detent for rotatable knob

ABSTRACT

A roller pump including a stator and a rotor assembly disposed within the stator. The rotor assembly includes a rotor hub, a first roller slide and a second roller slide slidingly disposed within the rotor hub. Each of the roller slides rotatably supports a roller. An occlusion adjustment knob for adjusting a radial position of the first and second roller slides and a magnetic detent assembly for providing an audible indicator as the occlusion adjustment knob is rotated.

This application is a divisional of application Ser. No. 10/077,769,filed on Feb. 20, 2002, now U.S. Pat. No. 6,607,363.

TECHNICAL FIELD

The present invention is directed to a detent assembly for a rotatableknob, and more particularly, to a magnetic detent assembly for providingaudible feedback during the rotation of an occlusion adjustment knob ona peristaltic pump.

BACKGROUND OF THE INVENTION

Peristaltic pumps are commonly utilized in medical applications. Forinstance, such pumps are often employed during cardiovascular surgery tofacilitate circulation of blood between a patient and a heart-lungmachine. Other common medical uses are the transfer of blood between apatient and a kidney dialyzer, and intravenous feeding of IV solutions.Generally, peristaltic pumps are simply structured, generate a constantflow, and employ disposable tubes as a member for fluid transfer.

Peristaltic pumps are relatively simple in construction and typicallyinclude a housing having rollers which progressively compress a flexibletube at spaced intervals against an arcuate surface or raceway so as toflatten or locally reduce the cross-sectional area of the tube. In thismanner, fluid leading to the flexible tube is continuously forcedthrough the flexible tube by one or another of the rollers as itproceeds along the flexible tube over the arcuate surface or raceway.

A conventional roller pump 10, as shown in FIG. 1, comprises a drivemechanism 14 furnished with a drive shaft 12, a rotating shaft 16 whichrotates according to the rotation of drive shaft 12, and a hollow pumphead 20 fixed to a housing 18 to which drive mechanism 14 is attached.This pump head 20 integrally incorporates a bearing block 24 throughwhich rotating shaft 16 is inserted and rotatably supported by a pair ofbearings 22 and a stator 26 arranged on the upper portion of bearingblock 24. On the upper surface of stator 26 is formed a recess 28through which the upper end of rotating shaft 16 is protruded. Whilethis recess 28 is radially and outwardly spaced at a certain distancefrom the outer circumferential surface of rotating shaft 16, its innercircumferential surface 28 a is coaxial with rotating shaft 16.

A rotor assembly 30 is attached to the upper portion of rotating shaft16 in such a way as to be placed inside recess 28 of stator 26 and tostay opposite the inner circumferential surface 28 a thereof. This rotor30 is fixed to rotating shaft 16 through a bolt 32, and is soconstructed as to integrally rotate along with rotating shaft 16. On theouter circumferential surface of rotor 30, at least one roller 34 isarranged so as to rotate about its own axes. A tube 36 which is filledwith blood or other fluid material is placed between rotor 30 and stator26. Tube 36 is clamped between respective rollers 34, which are attachedto rotor 30, and inner circumferential surface 28 a of stator 26,thereby maintaining tube 36 in a closed state at the point at which itis clamped.

Thus, in a conventional roller pump 10, rotor 30 is rotated by therotational motion of rotating shaft 16 driven by drive mechanism 14, andthe clamped portions of tube 36 move according to the revolution ofrollers 34 around rotating shaft 16. Therefore, fluid inside tube 36 istransferred according to the revolution of rollers 34. The rate ofrotation of the rotating shaft 16 and hence the rollers 34 is normallyadjustable so that the pumping rate of the fluid within tube 36 can beadjusted. However, the pumping rate can also be adjusted by adjustingthe degree to which the rollers compress the flexible tube. This can bedone in peristaltic pump assemblies by providing an adjustment mechanismfor adjusting the distance between the axes of the rollers and hence thedistance between the roller surface and the inner circumferentialsurface 28 a of stator 26. Another important reason for peristalticpumps to be adjustable in this fashion is that the compressibility,size, and other qualities of the flexible tube can vary considerably.

A rotor assembly 30′ having an adjustable occlusion capability, as shownin FIG. 2, comprises a rotor hub 40, and opposing roller slides 42, eachof which carries at least one roller 34 on the outer circumferentialsurface thereof. The roller slides 42 are extended or retracted from thehub 40 by turning the knob 44 on the top of the rotor hub. The extensionor retraction of the roller slides thereby changes the occlusion of theflexible tube within the peristaltic pump. The knob 44 is usuallyprovided with a detent assembly or some other type of mechanism whichprovides an audible feedback or signal as the knob is being rotated.

Typical detent assemblies disposed in the occlusion adjustment knob 44include spring loaded balls or plungers that ride against a plate ordisk with a series of slots or shallow holes. This type of detentmechanism provides both tactile and audible feedback as the plate movesover the spring loaded ball or plunger. However, both the tactile andaudible feedback can be significantly reduced to the point of beingnearly undetectable if there is significant resistance to the movementof the plate or disk. For instance, when there is a significantresistance to the rotation of the adjustment knob, such as caused byincreased compression of the flexible tube, for instance, the feel andsound of a spring loaded detent may be almost undetectable.

In addition, the metal-to-metal contact between the plate and the springloaded ball or plunger tends to create wear which in turn may affect theprecise positioning required by the spring loaded ball within the slotsor shallow holes of the plate. More particularly, the corners of thenotches or holes in a spring loaded detent plate or disk will tend tobecome rounded, changing the feel and sound of the detent as the platewears under contact. Commercially available spring loaded ball plungersoften have a 0.025 inch or less range of travel. The sound and feel of aspring loaded detent can also be quite sensitive to the force of thespring on the ball. Because of the sensitivity and limited range oftravel, the use of a spring loaded ball can require that the toleranceson the mechanical assembly be rather tight in order to assure that theball rides properly and consistently on the moving plate or disk.

Accordingly, there is a need in the art for a reliable detent assemblyfor providing an audible indication of rotation of a knob, which is notcompromised when resistance to movement is encountered and which doesnot require the precise positioning of the prior art.

SUMMARY OF THE INVENTION

A preferred embodiment of the present invention overcomes thesedrawbacks of the prior art by providing a roller pump comprising astator, a rotor assembly disposed within the stator, the rotor assemblyincluding a rotor hub, a first roller slide and a second roller slideslidingly disposed within the rotor hub, and each of the roller slidessupporting a roller. An occlusion adjustment knob is provided foradjusting a radial position of the first and second roller slides and amagnetic detent assembly provides an audible indicator as the occlusionadjustment knob is rotated. A further preferred embodiment of the rollerpump comprises a detent ring, with the magnetic detent assembly beingdisposed proximate to the detent ring. In a preferred embodiment, themagnetic detent assembly includes a base member having two sealedenclosures, each of the enclosures including a magnetically attractablemember and a magnet. Preferably, the magnetically attractable member isa sphere, such as a steel ball.

A further preferred embodiment of the present invention is directed to aknob assembly comprising a rotatable knob having an under surface and atop surface for gripping by a user, a notched plate rotatable with therotatable knob and arranged proximate to the under surface of therotatable knob, and a magnetic detent assembly disposed substantiallystationary proximate to the notched plate. Rotation of the rotatableknob and the notched plate over the magnetic detent assembly thusprovides a user with an audible indicator of rotation.

A still further preferred embodiment of the present invention provides amagnetic detent assembly comprising a base member having a top surfaceand a bottom surface, at least one magnetically attractable memberdisposed in a recess in the base member, and at least one magnetdisposed in the base member. The at least one magnetically attractablemember is movably contained in the recess between the top surface of thebase member and the at least one magnet.

BRIEF DESCRIPTION OF THE FIGURES

These, and other, objects, features and advantages of the presentinvention will become more readily apparent to those skilled in the artupon reading the following detailed description, in conjunction with theappended drawings, in which:

FIG. 1 is a cross-sectional view of a peristaltic pump as known in theprior art;

FIG. 2 is a perspective view of an alternative rotor assembly for aperistaltic pump as known in the art;

FIG. 3 is an exploded view of a rotor assembly for a peristaltic pumpaccording to the present invention;

FIG. 4 is an exploded view of a magnetic detent assembly according tothe present invention;

FIG. 5 is a bottom perspective view of a base thereof;

FIG. 6A is a bottom plan view of a base thereof;

FIG. 6B is a cross-sectional view taken along line VI—VI in FIG. 6A;

FIG. 6C is a top plan view of a base thereof; and

FIGS. 7A–7C illustrate the operation of the magnetic detent assembly ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

A peristaltic pump rotor assembly according to the present invention isshown generally by reference numeral 100 in the exploded view of FIG. 3.Rotor assembly 100 includes a pump or rotor hub 102, at least one andpreferably two opposing roller slides 104 a, 104 b, a roller 106 a, 106b disposed within each roller slide, respectively, and an adjustmentknob 108 for adjusting the occlusion of the flexible tube within thepump. The rotor assembly 100 is rotatably supported within a statorsimilar to that shown in FIG. 1 and as known in the art, and the innercircumferential surface of the stator forms the raceway for the rollers106 a, 106 b of the present invention. A main shaft 110 extendingthrough the rotor assembly 100 rotates according to the rotation of adrive shaft, which is rotated by a conventional drive mechanism, asshown in FIG. 1, for example.

Each of the roller slides 104 a, 104 b includes a plurality of recessesor channels 118 for receiving an extension spring 120. Each of thechannels 118 includes, preferably at an outer end thereof, a peg towhich the opposing ends of the springs are attached. As such, theopposing roller slides 104 a and 104 b are interconnected by a pluralityof springs 120. The rollers 106 a, 106 b are firmly held in the properposition within the roller slides 104 a, 104 b, respectively, by aroller shaft 124. Various bearings 126 and washers 128 may also be usedfor mounting the rollers 106 a, 106 b within the roller slides 104 a,104 b, respectively.

As shown in the illustrated embodiment, the rotor assembly 100 furtherincludes a cam block 138 which is spring loaded by a spring 142. A guidecollar 144 engages an upper surface of the cam block 138 and verticallyadjusts the position of cam block 138 through rotation of the adjustmentknob 108 and a screw adjustment member 146 which moves downward andthereby correspondingly moves the guide collar 144 in a downwarddirection. The cam block 138 includes opposing wedge-shaped projections148 which engage a corresponding dowel pin 149 on an inner surface ofeach roller slide 104 a, 104 b. Thus, as the adjustment knob 108 isrotated clockwise, for example, and screw adjustment member 146correspondingly moves downward so as to move guide collar 144 in adownward direction, cam block 138 is also moved downward such that thewedge projections 148 on the cam block 138 force the roller slides 104a, 104 b radially outward against the force of extension springs 120.

The adjustment knob 108 also includes an occlusion indicator ring 150and a detent ring 152 for providing an audible indication of the degreeof rotation of the knob 108. As shown, the detent ring 152 preferablyhas a scalloped periphery defining a plurality of teeth 153 withgenerally U-shaped cut-outs 155 therebetween. A plurality of retainingrings 154 and bearings 156 may also be provided.

Whereas the prior art included spring loaded balls or plungers thatinteracted with the cut-outs 155 in detent ring 152, the presentinvention provides a magnetic detent assembly, as shown by referencenumeral 200 in the exploded view of FIG. 4. The magnetic detent assemblyproduces audible clicks as the notched plate or detent ring 152, such asassociated with adjustment knob 108 of the peristaltic pump, is passedover the detent assembly 200. The notched detent plate 152 must be madeof a material that is attracted to a permanent magnet. The detentassembly 200 includes a base 202, at least one permanent magnet 204, andat least one ball 206, preferably made from steel or other magneticallyattracted material. The base 202 is preferably made from a material thatis not attracted to the permanent magnet.

Referring also to FIGS. 5 and 6A–6C, a preferred embodiment of themagnetic detent assembly 200 is more clearly illustrated. The base 202has a generally U-shaped configuration defined by a center portion andtwo extending legs, with recesses 208 a, 208 b disposed in eachrespective leg. In a bottom surface of each recess 208 a, 208 b isformed a ball receiving recess 216. A ball 206 is disposed in each ofthe recesses 216 within recesses 208 a, 208 b, and then a permanentmagnet 204 is placed thereover. A lid 210 is then disposed over each ofthe magnets to seal the magnet and ball within each recess in the base202. Ultrasonic welding may, for example, be used to seal the lid to thebase. In a preferred embodiment, the ball receiving recesses 216 have alongitudinal length/of approximately 0.2 inches and a steel ball havinga diameter of approximately 3 mm is disposed therein. Thus, the ballwill move from one side of the recess to the other side of the recess asthe notched plate passes thereover, as explained in greater detailbelow. The ball recesses 208 a, 208 b have a depth of approximately0.122 inches +/−0.002 tolerance. The overall length L of the detentassembly is approximately 1.816 inches and the overall width W thereofis approximately 0.641 inches, while the height H of the detent assemblyis approximately 0.410 inches. As should be apparent to one skilled inthe art, these specific dimensions are merely exemplary, and other sizesand shapes could, of course, also be used within the scope of thepresent invention to obtain the desired audible indication signal.

The lid 210 preferably has a notch 212 for receiving a post 214 formedon the base 202. It is this post 214 which is melted during the use ofultrasonic welding to thereby hold the lid to the base.

The operation of the detent assembly 200 can be described as followswith reference to the schematic illustrations of FIGS. 7A–7C. As theknob 108 is rotated, and notched plate 152 rotates therewith, the steelball 206 is pulled toward the nearest tooth 153 in the notched plate 152(i.e., tooth A). The magnetic permeability of a material such as steelis far greater than that of air, therefore the magnetic flux of thepermanent magnet will travel primarily through the nearest tooth of thenotched plate, and the force induced by this field will tend to pull thesteel ball 206 between the magnet 204 and the tooth 153. As the notchedplate 152 moves to the left over the substantially stationary magneticdetent assembly 200, as the rotatable knob 108 is turned, at some pointmore magnetic flux will travel through the next tooth 153 to the right(i.e., tooth B) and the steel ball 206 will be pulled to the right sideof the recess 216 in the base 202. The ball 206 will be pulled quicklyto the other side of the recess 216 and in so doing will make a clickingnoise as the ball 206 hits the side of the recess 216. As the notchedplate 152 continues to travel to the left, the ball follows the toothfrom the right to the left side of the recess 216 in the base 202. Thesequence of operation described above repeats with the ball makinganother clicking noise as it moves from tooth B to tooth C. If thedirection of the plate travel were reversed such that the plate moved tothe right, the operation of the detent would mirror that describedabove. In this case, the ball would make clicking noises as it hits theleft rather than the right side of the recess.

As an advantage of the magnetic detent assembly of the presentinvention, the clicks produced by the magnetic detent are much lesssensitive to resistance to the movement of the notched plate than aspring loaded detent. Whereas the feel and sound of a spring loadeddetent may be almost undetectable when there is significant resistanceto the rotation of the adjustment knob, the sound of the magnetic detentof the present invention remains substantially the same regardless ofthe level of resistance to the knob rotation. Moreover, the magnet andthe ball can be sealed in the base and are therefore less susceptible todirt and corrosion than a spring loaded detent. Similarly, minimal andperhaps no wear occurs as the notched plate moves over the detentassembly because there is no metal to metal point contact.

A magnetic detent assembly 200 has been implemented in connection withthe rotation of the adjustment knob 108 on the rotor assembly of aperistaltic pump. As the adjustment knob 108 is rotated, the span of therollers is adjusted, thereby changing the occlusion of the tube in thepump. The magnetic detent assembly 200 is designed to float in thevertical direction on the pump tongue. The detent assembly ismagnetically held to the bottom surface of the adjustment knob 108 andthe notched plate 152 moves directly over the detent assembly.Therefore, the function and sound of the magnetic detent is notsensitive to the tolerances between the various parts on which thenotched plate and the base of the detent assembly are mounted, as thebase will magnetically ride on the notched plate. In addition, it hasbeen found that the sound of the detent is consistent regardless of thedegree of tube occlusion and the resistance to the rotation of theadjustment knob. The magnetic detent assembly preferably includes twodetents, that is, first and second steel balls 206, one in the bottomrecess 216 of each of the recesses 208 a, 208 b, which are disposed oneach side of the pump tongue. The two detents are preferably used toincrease the resolution of the detent, and the number of clicks perrevolution of the knob thus increases by a factor of two. It is alsopossible to further increase the number of clicks per revolution byincluding additional detents in the design.

While the above described magnetic detent assembly has been illustratedwith respect to a preferred embodiment and use within an occlusionadjustment knob for a peristaltic pump, it should be apparent to oneskilled in the art that the applications of the detent assembly extendfurther to other devices and situations within the scope of the presentinvention.

1. A knob assembly comprising: a rotatable knob having an under surfaceand a top surface; a notched plate rotatable with said rotatable knoband arranged proximate to said under surface of said rotatable knob; amagnetic detent assembly disposed substantially stationary proximate tosaid notched plate, wherein said magnet detent assembly includes a basemember having at least one sealed enclosure, said at least one enclosureincluding a magnetically attractable member and a magnet; whereinrotation of said rotatable knob and said notched plate over saidmagnetic detent assembly provides a user with an audible indicator ofrotation.
 2. The knob assembly of claim 1 wherein said magneticallyattractable member is a sphere.
 3. The knob assembly of claim 2 whereinsaid sphere is a steel ball.
 4. The knob assembly of claim 1 whereinsaid base member includes a first recess for receiving said magnet. 5.The knob assembly of claim 4 wherein said first recess includes a secondrecess therein, said second recess dimensioned for receiving saidmagnetically attractable member.
 6. The knob assembly of claim 1 whereinsaid magnetic detent assembly has a central area and a leg extendingfrom each end thereof, thereby defining a generally U-shapedconfiguration.
 7. A magnetic detent assembly for generating audiblefeedback during relative movement past a magnetizable structure,comprising: a base member having a top surface and a bottom surface; atleast one magnetically attractable member disposed in a recess in saidbase member, said recess being elongated between a pair of oppositesides formed within said base member; and at least one magnet disposedin said base member between said recess and said botton surface; whereinsaid at least one magnetically attractable member is movably containedin said recess between said top surface of said base member and said atleast one magnet, and wherein said at least one magnetically attractablemember strikes at least one of said opposite sides during movement ofsaid magnetizable structure past said top surface to generate saidaudible feedback.
 8. The magnetic detent assembly of claim 7 whereinsaid recess is formed in a bottom surface of a magnet receiving recessin said base member.
 9. The magnetic detent assembly of claim 7 whereinsaid at least one magnetically attractable member comprises a sphere.10. The magnetic detent assembly of claim 7 where said at least onemagnetically attractable member is formed from steel and said basemember is formed from a plastic material.